American Express Membership Rewards - PRG to Plat Upgrade, when does 3x airfare bonus end?

I'm PRG and planning to upgrade to Plat for the 25k MR bonus and lounge benefits before I have to do a bunch of travel in September. I would like to book my flights with the PRG card and get the 3x airfare bonus before switching to Plat. My question is, can this be done, or are points only calculated at the end of your statement period?

E.g., if I book the flights now and then in two weeks upgrade to Plat, will my statement's worth of MR points be calculated using the PRG rates or the 1:1 Plat rate? I suppose it depends on if I book using the PRG before my statement ends, then upgrade, but if anyone has any experience upgrading in the middle of their monthly statement, please let me know. Tyia.

If I were you I'd just apply for the Platinum separately rather than upgrading. Just keep the PRG until the fee's about to come due and then cancel it if you don't want it anymore.

This does once again remind me that I wish Amex would introduce a "Premier Rewards Platinum" card. It's pretty bizarre that the top-of-the-line card is not really worth using for spending.

If I were you I'd just apply for the Platinum separately rather than upgrading. Just keep the PRG until the fee's about to come due and then cancel it if you don't want it anymore.

This does once again remind me that I wish Amex would introduce a "Premier Rewards Platinum" card. It's pretty bizarre that the top-of-the-line card is not really worth using for spending.

I thought consensus was that if you're currently in line for a Plat upgrade and have PRG, you can't get 50k by applying outright for a separate Plat card? Please correct me, I'd love to keep both.

And totally agree re: Plat Rewards card.